Relay Chattering: Causes & Prevention

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SUMMARY

Relay chattering is primarily caused by insufficient power supply to the relay coil or oscillations in the coil signal. In specific cases, such as with A/C units, pressure fluctuations from reciprocating compressors can lead to this issue. Solutions include decoupling the coil drive from the relay load, ensuring adequate power supply, and utilizing better local AC coupling capacitors. Addressing these factors effectively prevents relay chattering.

PREREQUISITES
  • Understanding of relay operation and characteristics
  • Knowledge of electrical circuit design principles
  • Familiarity with power supply requirements for relay coils
  • Experience with AC coupling techniques in electronic circuits
NEXT STEPS
  • Research methods to decouple relay coil drive from load circuits
  • Learn about power supply design for relay applications
  • Explore AC coupling capacitor selection and implementation
  • Investigate the impact of mechanical vibrations on relay performance
USEFUL FOR

Electrical engineers, technicians working with relay systems, and anyone involved in designing or troubleshooting A/C units and other relay-driven applications.

kal22
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What causes relay chattering and what can be done to prevent it?
 
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What are your thoughts? What specific circuit are you working with? Is this homework?
 
I've dealt with a relay chattering on an A/C unit due to the pressure fluctuations of the reciprocating compressor on the pressure switch that pulled-in the relay...

...so this is very situation specific.
 
How is 'chattering' defined? I mean, as in frequency and/or mechanical vibration. If it's really fast, like a buzzer, I'm wondering about a bad connection that causes the primary circuit to fail when the armature moves...?
 
Two common reasons:
1. When the relay 'makes' the new system load causes a step current drop in the relay drive coil due to an insufficiently sourced system power supply. This causes the relay to 'break', the open load allows the coil current to recover closing the relay again an so on. Decouple the coil drive from the relay load to correct: more head room on your system power supply, separate power for coil and load (usually is anyway for a relay - that's the point) or better local AC coupling caps (careful - can be complicated as you can just create more problems in a tank circuit w/ the coil and caps)
2. A simple oscillation of some kind on the coil (signal side) independent of the load.
 

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